In general, a vibration damping material for absorbing vibration energy is used in areas where vibration occurs, in a vehicle, a railway car, aircraft, a household appliance, an OA apparatus, a precision apparatus, a building machine, a construction/building, shoes, a sport gear, and the like, in order to damp the vibration.
As a material for absorbing vibration energy, the material being used as a vibration damping material, there have been known, in addition to a polymeric material, a lead core and an oil damper that utilize plastic deformation, for example. However, lead is included in substances to be controlled under environment-related regulations that have been established in recent years, and hence the use of the lead core has been becoming difficult. Meanwhile, the oil dumper has problems in that the direction in which vibration is absorbed is limited and in that a small oil dumper is difficult to produce because the oil dumper needs a complex construction. Thus, a vibration damping material utilizing a polymeric material is widely used in general as a material that can be easily used without causing the above-mentioned problems.
As the kind of a polymeric material that is used as a vibration damping material, there are disclosed rubber materials such as butyl rubber and NBR, soft vinyl chloride-based materials each obtained by adding a plasticizer to a vinyl chloride-based resin, polyesters, polyamides, polyvinyl compounds, polyurethanes, polyolefins, and the like. In addition, there are disclosed many forms of resin compositions each obtained by adding a filler made up of an inorganic substance or an organic substance for improving vibration dumping performance, mechanical strength, and durability.
There are disclosed, particularly as a vibration dumping material that includes a polyester resin as a base substance, for example, a vibration dumping material made up of a polyester resin alone (Patent Documents 1, 2, and 3), a vibration dumping material obtained by blending polyester resins having different glass transition temperatures with each other (Patent Document 4), a vibration dumping material obtained by adding a curing agent to the vibration dumping material in Patent Document 4 (Patent Documents 5, 6, 7, and 8), and a resin composition obtained by adding an inorganic substance (Patent Document 9), in particular, adding a glass fiber (Patent Documents 10 and 11), to the above-mentioned polyester resin or to a complex resin produced by combining the polyester resin with another resin. However, those materials known until now do not necessarily satisfy all levels required from the standpoints of vibration dumping performance, processability, toughness, and the like, and hence those materials need further technical improvements.
Meanwhile, there is disclosed a resin composition in which mica is dispersed in a polyester resin, in particular, a polyester resin characterized in that the number of skeleton carbon atoms between functional groups is odd (Patent Document 12). The resin composition has high vibration dumping performance at around room temperature, and is a promising vibration dumping material. Thus, the resin composition can be used as a material exerting high vibration dumping performance in a region having a higher temperature than room temperature by adjusting the composition of monomers each constituting the polyester resin. However, there remains a problem that because the flexibility of the polyester resin is insufficient, when the resin undergoes processing, the resin produces breaks and cracks. Thus, it is not possible to say that the polyester resin sufficiently satisfies the requirement that high vibration dumping performance should be exerted in a wide temperature region.
Patent Document 1: JP-A-62-295949    Patent Document 2: JP-A-5-230195    Patent Document 3: JP-B-3311849    Patent Document 4: JP-A-6-031853    Patent Document 5: JP-A-2003-221496    Patent Document 6: JP-B-2613502    Patent Document 7: JP-B-2623316    Patent Document 8: JP-B-3117798    Patent Document 9: JP-B-3780385    Patent Document 10: JP-B-2925636    Patent Document 11: JP-B-3075905    Patent Document 12: JP-A-2006-052377